Air-gap insulated exhaust manifold

ABSTRACT

An air gap insulated exhaust manifold includes several inlet tubes which are fit into one another so as to be movable relative to each other and complement each other so as to constitute a collecting chamber. The inlet tubes are surrounded by an outlet tube, an air gap resulting between the inlet and outlet tubes. Two shell-type intermediate plates are provided in this air gap and complement each other so as to constitute a hollow body, which prevents that any leakage flows directly hit the outlet tube. The intermediate plates are produced by deep-drawing a pimpled foil.

The invention relates to an air gap insulated exhaust manifold comprising at least one cylinder-side inlet tube and at least one exhaust pipe-side outlet tube, the tubes being arranged into one another in the region of a collecting chamber, forming an air gap which surrounds the collecting chamber at least in part.

With exhaust manifolds, in particular for gasoline-operated engines, the tubes are subject to enormous thermal loads. This is why so-called air gap insulated exhaust manifolds exist, as they are described in DE 197 52 773 A1, for instance. In the region of the manifold usually several inlet tubes are brought together, which are connected to the engine block in the region of the cylinder outlets by means of flanges. These inlet tubes open into a collecting chamber, from where the gas flows into an outlet tube which is connected to the exhaust gas tube by means of a flange or constitutes a portion thereof. The inlet tube(s) and the outlet tube are put into each other such that a thermally insulating air gap is formed between them in the region of the collecting chamber. In this context, it is of secondary importance and a matter of concept which one of the two tubes forms the inner and which one the outer tube. It is usual that the inlet tube(s) and the outlet tube are arranged into one another so as to be movable in the broadest sense, in order to be able to compensate for the enormous linear expansion of the tubes in operation, whereby the load of the tubes is supposed to be reduced, too. To this end, inlet and outlet tubes are usually welded to a flange at the side of the engine block. The inner tube, however, freely projects into the interior of the outer tube, so that the tubes can move relative to each other during thermal expansion without any chance that warping occurs. The inlet and outlet tubes are not arranged so as to be gas-tight relative to each other, since several inlet tubes are usually put into one another so as to be movable relative to each other for length compensation. This has the effect that the outer tube is impinged in the region of the collecting chamber by unavoidable leakage flows. It is in particular at the leakage points of the internal tube(s) where the outer tube will have a so-called hot spot, i.e. a punctual area with maximum thermal load.

It is an object of the invention to reduce the thermal loads of the outer tube in the region of the collecting chamber in a very simple manner.

For this purpose, the exhaust manifold of the type initially mentioned provides at least one intermediate plate being arranged in the air gap. This intermediate plate usually has no load-bearing function, but serves for shielding the outer tube.

This is why the intermediate plate can be advantageously designed so as to be extremely thin, with a maximum thickness of 0.3 mm, preferably 0.15 mm; in a sense, it is just a sort of sandwiched foil. During experiments it has been shown that this foil-like, thin sheet metal on its own is completely sufficient in order to avoid the hot spots.

It will be preferred that several intermediate plates are provided.

These several intermediate plates may completely or for the most part surround the collecting chamber, hence, function as an intermediate wall between the outer tube and the inner tube.

Preferably, the intermediate plates have a shell-like construction and, according to a further embodiment, can complement each other so as to constitute a hollow body. If necessary, it would also be possible to form the hollow body from one intermediate plate. In this context, “shell-like” construction stands for a non-even plate having an arched cross-section, preferably a semicircle cross-section.

It is sufficient if the intermediate plates are simply fit into one another at their contact edges.

The intermediate plates or shells do not have to be fastened to each other, for instance brazed or welded; only the process of fitting one into another will already be sufficient to form a hollow body which for the required purposes is closed to a sufficient extent. It turned out, that this hollow body does not have to be gas-tight or largely gas-tight.

The intermediate plate has a thickness which is considerably smaller and flexibility being considerably larger than that of the inlet or outlet tubes, so that the intermediate plate in the preferred embodiment has no load-bearing function at all. The maximum thickness amounts to 0.3 mm, preferably 0.15 mm at most. Experiments have shown that even a maximum limit of 0.10 mm results in an excellent thermal insulation from the outer to the inner wall.

The exposed inner side of the outer wall, delimiting the air gap, which is formed by the inlet or outlet tube (depending on which one of the tubes lies on the outside), is covered by the intermediate plate to at least 80%, the latter in particular being situated in front of the hot spots.

Owing to the intermediate plate, the air gap can be subdivided into an inner and an outer portion, improving hereby the insulating effect.

According to one embodiment, the intermediate plate has protrusions which serve as spacers and with which it has a small, for instance a punctual, area of contact with the inlet and/or outlet tube, so that it may be clamped between the two tubes.

Production of the intermediate plate can be executed in a very simple manner, e.g. by deep-drawing, with a so-called pimpled foil being preferably used here, i.e. a foil which is not plane but has an uneven surface, the rear side defining the form-related negative of the front side. Due to this irregular surface, sufficient material will still be available during deep-drawing so that the risk of crack formation is reduced.

The intermediate plate preferably should have a form corresponding to the external wall of the collecting chamber. In this context, the term “corresponding” means that the foil should not have contact over the full surface area at the inner side of the outer wall, of course, but for the most part has a uniform distance thereto.

It turned out, that the intermediate plate simply has to be inserted in the air gap without being fastened to the inlet or outlet tube. Merely the clamping effect between the two tubes is sufficient, as has already been explained above.

According to the preferred embodiment, not only one inlet tube is provided, but there are several cylinder-side inlet tubes which open into the collecting chamber being fit into one another so as to be movable relative to each other.

It is preferred here that the intermediate plate surrounds all inlet tubes which are provided in the region of the collecting chamber.

Further features and advantages of the invention will be apparent from the following description and the following drawings to which reference is made and in which:

FIG. 1 is a schematic longitudinal sectional view through an exhaust manifold according to the invention,

FIG. 2 is a sectional view along line II-II in FIG. 1, and

FIG. 3 is a sectional view along line III-III in FIG. 1.

FIG. 1 shows an air gap insulated exhaust manifold which connects three cylinder-side inlet tubes 2, 4, 6 with each other. The cylinder outlets are symbolized by the circles 8. Each cylinder 8 has its own inlet tube 2, 4, 6 associated with it. The inlet tubes 2, 4, 6 have a portion 9 which comes from the cylinder and with which they are welded to the cylinder block flange 11 (FIG. 3), and a freely protruding portion with which they further extend into an exhaust pipe-side outlet tube 10 (FIGS. 2 and 3). The exhaust pipe-side outlet tube 10 consists of upper and lower shells 12, 14 and has an outlet-side flange 16 to which an exhaust gas tube is fastened. On the inlet side, the outlet tube 10 likewise is welded to the cylinder block flange 11. The outlet tube 10 surrounds the inlet tubes 2, 4, 6 in the region where these merge into each other in terms of flow. In this arrangement, the inlet tubes 2, 4, 6 are fit into one another. For this purpose, the middle inlet tube 4 has lateral, enlarged reception openings pointing in opposite directions and movably receiving the left and right inlet tubes 2, 6. In the interior of the inlet tubes 2, 4, 6 which are fit into one another, specifically in the region of the outlet tube 10, a collecting chamber 18 is formed which essentially has an elongated cylindrical shape and extends from the left-hand portion of the left inlet tube 2 as far as to the right-hand portion of the right inlet tube 6 in the drawing plane in FIG. 1.

Between the inlet tubes 2, 4, 6 and the inner side of the outlet tube 10 an air gap 20 is formed which has an approximately uniform thickness and serves the thermal insulation.

Apart from thermal insulation, this air gap 20 is intended to provide a free expansion of the inlet tubes 2, 4, 6 relative to the outlet tube 10, because the inlet and outlet tubes are fastened to each other only at one end and, hence, are movably arranged into each other beyond that end.

The air gap surrounds the collecting chamber 18 on all sides.

Two shell-shaped, deep-drawn intermediate plates with a maximum thickness of 0.3 mm (just 0.1 mm in the embodiment which is shown) are arranged in the air gap 20 and entirely surround the collecting chamber 18. In this arrangement, an upper intermediate plate 22 is fit into a lower intermediate plate 24, with the intermediate plates 22, 24 being slightly clamped in the region of their contact edges 26 (FIG. 2).

The intermediate plates 22, 24 cover the inlet tubes 2 to 6 immediately after penetrating the outlet tube 10 (FIG. 3), and extend as far as to the flange 16, as can be seen in FIG. 1.

The intermediate plates 22, 24 complement each other so as to form a very flexible, thin hollow body which is clamped between the inlet tubes 2 to 6 and the outlet tube 10, without being permanently fastened to the tubes and without having any load-bearing function.

Spacers in the form of punctual protrusions 28, having been produced during deep-drawing of the intermediate plates 22, 24, serve for making contact and maintaining the distance of the intermediate plates 22, 24 to the inlet tubes 2 to 6 and the outlet tube 10, so that the air gap 20 is subdivided by the intermediate plates in an inner and an outer portion 30, 32.

The intermediate plates 22, 24 are produced by deep-drawing a foil of uniform thickness but with a slightly dimpled surface, so that material can flow during deep-drawing.

In some embodiments the inlet tubes 2 to 6, the outlet tube 10 and/or the intermediate plates 22, 24 may be multi-layered composite parts which consist of several superimposed, foil-like metal sheets which are connected with each other and have a thickness of about 0.05 to 0.1 mm each.

In driving operation, hot exhaust gas flows out of the cylinders via the inlet tubes 2 to 6 into that part of the exhaust manifold in which the manifold is configured two-shelled, and arrives at the collecting chamber 18. Due to the inlet tubes 2 to 6 being supported so as to be movable relative to each other, leakage flows will occur, so that the exhaust gas in effect would impinge the inner side of the outlet tube 10 with high speed and result in hot spots at these places. However, as the intermediate plates 22, 24 cover almost the entire inner side of the wall (outlet tube 10) delimiting the air gap 20 outwards, the leakage flows hit the intermediate plates 22, 24. It may be possible in fact, that leakage flows occur in the region of the contact edges 26, but these can be neglected with respect to the thermal load of the outlet tube 10.

The intermediate plates are made of temperature-resistant material, e.g. AISI 309.

Through the use of the intermediate plates 22, 24 it is also conceivable to use materials for the outlet tube 10 which have a somewhat lower temperature stability. 

1.-16. (canceled)
 17. An air gap insulated exhaust manifold, comprising: at least one cylinder-side inlet tube, at least one exhaust pipe side outlet tube spaced apart from the at least one cylinder-side inlet tube in the region of a collecting chamber to form an air gap which surrounds the collecting chamber at least in part, and at least one intermediate plate arranged in the air gap.
 18. The exhaust manifold according to claim 17, wherein the at least one intermediate plate comprises a plurality of intermediate plates.
 19. The exhaust manifold according to claim 18, wherein the intermediate plates are fit into one another at their contact edges.
 20. The exhaust manifold according to claim 17, wherein the at least one intermediate plate is/are shell-shaped.
 21. The exhaust manifold according to claim 17, wherein the at least one intermediate plate form(s) a hollow body.
 22. The exhaust manifold according to claim 17, wherein the at least one intermediate plate has a maximum thickness of 0.3 mm.
 23. The exhaust manifold according to claim 17, wherein the at least one intermediate plate has a maximum thickness of 0.15 mm.
 24. The exhaust manifold according to claim 17, wherein the at least one intermediate plate covers at least 80% of the exposed inner side of the outer wall delimiting the air gap.
 25. The exhaust manifold according to claim 17, wherein the at least one intermediate plate subdivides the air gap into an inner and an outer portion.
 26. The exhaust manifold according to claim 17, wherein the at least one intermediate plate has protrusions which contact at least one of the inlet and outlet tubes.
 27. The exhaust manifold according to claim 17, wherein the at least one intermediate plate surrounds the inner one of the two tubes in the region of the collecting chamber.
 28. The exhaust manifold according to claim 17, wherein the at least one intermediate plate is a deep-drawn foil which prior to deep-drawing has a pimpled surface.
 29. The exhaust manifold according to claim 17, wherein the at least one intermediate plate has a shape corresponding to the external wall which delimits the air gap.
 30. The exhaust manifold according to claim 17, wherein the at least one intermediate plate is inserted in the air gap without being fastened to the inlet or outlet tubes.
 31. The exhaust manifold according to claim 17, wherein the at least one cylinder-side inlet tube comprises a plurality of cylinder-side inlet tubes which open into the outlet tube and are fit into one another so as to be movable relative to each other.
 32. The exhaust manifold according to claim 31, wherein the at least one intermediate plate surrounds all of the plurality of inlet tubes in the region of the collecting chamber.
 33. The exhaust manifold according to claim 17, wherein the at least one inlet tube(s) and the at least one outlet tube(s) are connected with each other at one end only, and that the inner one of the two tubes freely projects in an unsupported manner into the interior of the outer one of the two tubes. 